Jig boring machines consist of a reciprocating boring tool and a table. The table, which typically moves in an x-y plane, holds a workpiece for drilling by the bore, which translates in parallel to a z-axis. The table may hold a jig for maintaining a particular mechanical relationship between the workpiece and the bore. Some jigs may rotate the workpiece in the x-y plane or tilt the workpiece about the x or y-axis In order to ensure the accuracy of the boring, the support table, the bore, and the jig must be calibrated.
It is known in the art to utilize an angle iron to calibrate a jig boring machine. The angle iron consists of three rectangular, dimensionally stable, flat plates. The first plate is disposed in parallel to the x-y plane, and has an edge disposed in parallel to the x-axis and an edge disposed in parallel to the y-axis. The second plate attaches at a bottom edge portion thereof to an edge of the first plate, and is disposed in parallel to a y-z plane. The second plate has an edge portion disposed in parallel to the y-axis and an edge portion disposed in parallel to the z-axis. The third plate is disposed in parallel to an x-z plane and attaches at a bottom edge thereof to a top surface of the first plate and at a side edge thereof to the second plate. The third plate has an edge portion disposed in parallel to the x-axis and an edge portion disposed in parallel to the z-axis. The third plate has an opening which functions as a handle.
To calibrate the jig boring machine, essentially two items must be checked--the jig boring machine and the jig. By attaching a dial indicating gage (i.e. a surface gage) to the bore, and mounting the angle iron to the jig, the jig boring machine may be calibrated by moving either the support table or the bore as explained below.
By placing the dial indicating gage upon the surface of the table and translating the table in parallel to the x-axis, the tilt of the table relative to the y-axis may be checked. Similarly, by placing the dial indicating gage upon the surface of the table and translating the table in parallel to the y-axis, the tilt of the table relative to the x-axis may be checked.
By placing the dial indicating gage along an edge of the first plate arranged to be in parallel to the x-axis and translating the table in parallel to the x-axis, the tilt of the jig relative to the x-axis may be calibrated. By placing the dial indicating gage along a surface of the second plate arranged to be in parallel to the x-z plane and translating the bore along that surface in the z-axis, a first component of the alignment of the bore to the z-axis may be checked.
Similarly, by placing the dial indicating gage along an edge of the first plate arranged to be in parallel to the y-axis and translating the table in parallel to the y-axis, the tilt of the jig relative to the y-axis may be calibrated. By placing the dial indicating gage along a surface of the second plate arranged to be in parallel to the y-z plane and translating the bore along the surface in the z-axis, a second component of the alignment of the bore to the z-axis may be checked.
When using a jig which tilts about the x or y-axis, the accuracy of the angle of tilt must be calibrated. Typically, the jig is tilted a given degree and a sine bar or plate is mounted on the jig after the angle iron is removed.
The sine bar or plate is utilized for accurately measuring angles or for locating work to a given angle. Two buttons of the same diameter and at a known distance apart are mounted on a center line. The sine bar rotates about one button. The operation of the sine bar is based on the trigonometric relationship that the sine of an angle is equal to the opposite side divided by the hypotenuse. Hence, if the hypotenuse is known, the angle may be determined by measuring the height of the opposite side, dividing it by the known figure, and referring to trigonometric tables. Measurement of the unknown side is accomplished by the use of a height gage or precision blocks. The tilt of the table may be calibrated by subtracting the given angle from 90.degree., adding the proper precision blocks to one end of the sine bar so the the sine bar (i.e. the hypotenuse) is disposed at the subtracted angle (if properly calibrated, the sine bar would be parallel to the x-y plane), placing the dial indicating gage along the sine bar, and translating the support table parallel to the x-axis.
The present method is time consuming and requires a plurality of set-ups. Hence, a new calibration tool is sought.